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IndustryArena Forum > Mechanical Engineering > Mechanical Calculations/Engineering Design > Moving table (fixed gantry) with two ballscrew

Thread: Moving table (fixed gantry) with two ballscrew

1. Re: Moving table (fixed gantry) with two ballscrew

I bought a fraction of 3-5mm. I'm drying the sand now.
In test 2, the ratio of the two fractions is 50% of the volume of the test volume (1000 ml).
This is absolutely wrong. Also the ratio of 70% Vf (1-2mm) to 30% Vf(0.10-0.25mm) is wrong. We cannot thinking up arbitrary ratios. Even with calculation at 10 times the diameter difference between the small and large fraction - the volume ratio is 1000 times.

It is most appropriate to determine the ratio when mixing multiple fractions experimentally. We want to get the highest coefficent of packing.
So, for me, the correct method is the following:

The test volume is 1000 ml.
1. Fill the container with 1000 ml of the coarsest fraction.
2. We start adding small portions from the next finer fraction (recording their volumes) and stirring, mixing, vibrating etc. The fine fraction particles are inserted between the voids of the coarse particles. The volume of 1000 ml should remain unchanged (constant). We fill and vibrate until we can no longer keep the volume of 1000ml constant and it starts to increase.
This means that there is no more space (voids) between the coarse particles. We calculate the recorded quantities (volumes) of the fine fraction inserted and thus calculate the volume ratio.
3. If there is a third fraction - proceed as in point 2. Keep the total (mixed volume) constant - 1000 ml.

2. Re: Moving table (fixed gantry) with two ballscrew

Morning Ivan - So what are you aiming at? Industry information tells us that 70%Vf is about the top figure and you have achieved that. Are you chasing 90%? Industry has settled on 70%Vf for a reason. One of these is scaling. You maybe able to work hard and get your 1000ml sample up higher but then, will it scale and get you the result with a 150kg batch? You can't mix big batches as well as small batches unless you have big equipment. The Basetek company have videos of hugh mixers and graders making very large batches. They would happily make EG at higher Vf as the gravel is cheaper then the resin. The other thing is that by back calculating from their data they are under filling the resin. Perhaps that's the trade off. They are happy to make a sponge vs a solid to save \$\$\$ on the resin. From my composites experience using stitched cloth and UD fibres which are already in a state of high order and using 6 atms pressure in an autoclave we don't get past 60%Vf easily. So why not be happy with 70%Vf and move forward? Back to scaling. Boats have to be surveyed and they use test panels for the engineering certification. They are 600x600mm usually. I have been making these and helping boat builders make these for 30 years. Its always a concern that we make a 20m plus boat using tonnes of material based on a one off small panel. Over the years I have figured out how to make panels very well. I can instruct builders to lay cloth a particular way, use vacuum a particular way, build the bag like this not like that etc. This results in exceptional good figures. But I don't like doing that because it does not scale to the boat. You can't scale all of those hints into a big boat build easily. Maybe same with your samples. So what are you aiming at in terms of Vf and your E?

Did you see the Koehler article I attached to the EG thread? may help in your research... Peter

3. Re: Moving table (fixed gantry) with two ballscrew

Hi Peter.
I don't know how to answer you. Just looking for the maximum with affordable funds. I didn't know the maximum was about 70%. If so - well.
Just from reading a lot of EG threads where there are posts for 90% aggregates and 8-10% resin - I decided to strive for that. Now I see that this is impossible.
I thing that It's not a bad to experiment and find the best. I believe that these tests will not only be useful to me. So they are worth the time lost

I didn't make it in the afternoon . It took me quite a few hours. And half the tests - I repeated.
What I wrote in my previous post was not confirmed. Even the opposite. This in the particle schematic picture is true only in theory. In practice, with small amounts of fine particles, they do not get trapped in the holes between coarse particles. The fine particles just fall to the bottom. No uniformity is obtained.
Test 5 shows this - a bad result. My scale is not very accurate. But this has no relation to the % of quartz volume fraction (Vf).
That is for now.

4. Re: Moving table (fixed gantry) with two ballscrew

Hi Ivan - Yes segregation is a big problem when aiming at high packing factors. More reading this morning and most concrete mixes in reality are about 70% Vf maybe 75% in the lab. The theories that get to 90%Vf are based on spheres with no friction and that's the problem. Real particles are not spheres and they have sharp edges that stop them packing down. So what's your next step? Now you know the practical limits? regards Peter

5. Re: Moving table (fixed gantry) with two ballscrew

Morning Peter.
First I will complete the design with all the details (energy chains, inductive sensors, etc. Then I'll do a real resin test (Test 11). I hope the real 70% Vf (no 75%).
About the large casting volumes. I'm a builder engineer by profession. I have different big concrete mixers (from 100 to 300kg). No problem for mixing.

6. Re: Moving table (fixed gantry) with two ballscrew

Afternoon here Ivan Good keep us up to date. I too am re starting a moulded cnc mill design so thanks for your help so far. I'm trying to get the biresin here in OZ but seems sika don't stock it here. The usual will be fine...Peter

7. Re: Moving table (fixed gantry) with two ballscrew

Hi Peter. Try contact here. They may agree to send to Australia.
https://www.compositeshop.de/xoshop/...d-returns.html

I can buy you cr83 here in Bulgaria and send it to you. But I suspect the shipping will be very expensive.

8. Re: Moving table (fixed gantry) with two ballscrew

Hi Ivan -Thanks for offer but yes its expensive Europe to Oz. I found some milled carbon fibre in france that I wanted. 20 euro/kg for the sample and 180 euro to get it here. I'll have to wait until I can build that into a project. I'm waiting for the local sika people to see if they can get it in. Otherwise my usual epoxy will be fine. Peter

9. Re: Moving table (fixed gantry) with two ballscrew

Originally Posted by Ivan_1966
Hi Peter.
I don't know how to answer you. Just looking for the maximum with affordable funds. I didn't know the maximum was about 70%. If so - well.
Just from reading a lot of EG threads where there are posts for 90% aggregates and 8-10% resin - I decided to strive for that. Now I see that this is impossible.
It's important to differentiate weight and volume here.

The EG threads talking about 90% aggregate and 10% resin are talking about the proportions in the mix by weight. They are not talking about packing fraction.

10. Re: Moving table (fixed gantry) with two ballscrew

Yes pippin88. You're right ! I didn't pay attention to the fact that there talks about weight.

11. Re: Moving table (fixed gantry) with two ballscrew

Hi Pippin and Merry Christmas - Yes Ivan and I have been working with both. Plus the industry information seems to point at they are under-filling the pack with resin. This maybe to save \$\$\$ or to create a porous pack vs a solid pack. We don't know. So EG makers need to understand the difference (volumes vs weight ratio) and then they can figure these things out correctly. Peter

12. Re: Moving table (fixed gantry) with two ballscrew

I’m as well preparing for a next level EG build so I just wanted to say kudos to this nice & interesting debate on EG.

Peter, have you maybe already been experimenting with some chopped UD carbon fibers in EG castings?

Aleksandar

13. Re: Moving table (fixed gantry) with two ballscrew

Hi Aleksandar - I have been infusing CF and epoxy for many years. By adding CF to "EG" do you mean adding CF to epoxy and sand or will it be just CF and epoxy? Standard CF is 210GPa stiffness. This will produce quite a stiff material if you can pack it well. CF is expensive so a good approach would be to use stitched fibre to lay in the mould as an outside skin, this maximises its stiffness then use sand on the inside for its weight. Regards Peter

14. Re: Moving table (fixed gantry) with two ballscrew

Originally Posted by peteeng
Hi Aleksandar - I have been infusing CF and epoxy for many years. By adding CF to "EG" do you mean adding CF to epoxy and sand or will it be just CF and epoxy? Standard CF is 210GPa stiffness. This will produce quite a stiff material if you can pack it well. CF is expensive so a good approach would be to use stitched fibre to lay in the mould as an outside skin, this maximises its stiffness then use sand on the inside for its weight. Regards Peter
Hi Peter,

Yes of course, together with sand.

Or maybe even better, yesterday I was thinking about using Alumina agregate premixed with helix shaped chopped carbon fiber & or maybe adding some quartz aggregate too...

Here I would like to ask, which shape of aggregate would you preffer? Due to some complex internal structure design and therefore better flow/stacking properties I’m planning to use round ball alumina agreggate...
Do you have any experience using round ones vs. stone chucks shaped?

Aleksandar

15. Re: Moving table (fixed gantry) with two ballscrew

Hi Alek - alumina is very stiff and will give you a very stiff mix. If you add chopped fibre to it, it will not pack as well due to the random fibers taking up lots of space. I suggest you just go with the alumina grit and epoxy so you get the best pack. If you can get alumina I wouldn't worry about quartz, Al203 is nearly 3x stiffer then SiO & stiffer then std modulus CF, so no point in having SiO in there.

The more things mixed it seems the worse things pack. Keep it simple and alumia grit and epoxy will do very well. Use a very thin epoxy something designed for infusion or casting, not laminating they are too thick. Brands are mentioned earlier....
Are you wet mixing or vacuum casting? Cheers Peter S

16. Originally Posted by peteeng
Hi Alek - alumina is very stiff and will give you a very stiff mix. If you add chopped fibre to it, it will not pack as well due to the random fibers taking up lots of space. I suggest you just go with the alumina grit and epoxy so you get the best pack. If you can get alumina I wouldn't worry about quartz, Al203 is nearly 3x stiffer then SiO & stiffer then std modulus CF, so no point in having SiO in there.

The more things mixed it seems the worse things pack. Keep it simple and alumia grit and epoxy will do very well. Use a very thin epoxy something designed for infusion or casting, not laminating they are too thick. Brands are mentioned earlier....
Are you wet mixing or vacuum casting? Cheers Peter S
Well OK, could be definetly true in case of not vacuuming the casting but that wouldn’t be my case. Everything will be vacuum casted maybe even in autoclave...

Anyways, as the pure Alumina is very expensive & hard to get in low quantities I was considering some high grade Bauxite aggregate.
It’s around 85-90% Al2O3 with some small amounts of:
- Fe2O3
- TiO2
- CaO+MgO
- R2O

Did you noticed any case using this aggregate with epoxy?

AS

17. Re: Moving table (fixed gantry) with two ballscrew

Hi Alek - Alumina, Alox, Corundum (aluminium oxide) blasting grit. The white alumina is dear but brown alumina is \$99AUD for a 25kg bag. White is \$160AUD per 25kg bag. SiO is free at the beach. Alox comes in 12 grit (1.7mm) to 320grit (0.05mm). Autoclave not needed your bauxite sounds fine. Peter

https://ferroecoblast.com/storage/ap...009_web_en.pdf

18. Originally Posted by peteeng
Hi Alek - Alumina, Alox, Corundum (aluminium oxide) blasting grit. The white alumina is dear but brown alumina is \$99AUD for a 25kg bag. White is \$160AUD per 25kg bag. SiO is free at the beach. Alox comes in 12 grit (1.7mm) to 320grit (0.05mm). Autoclave not needed your bauxite sounds fine. Peter

https://ferroecoblast.com/storage/ap...009_web_en.pdf
Hi Peter,

Ferro?rtali? is actually a company that’s 60km away from my workshop so that was a great info!
Need to check the prices vs China...

Questions:
1.) Were you ever doing some simulations between using sharp asymetric vs perfectly round shapes of aggregates?

2.) Since elctrified Bauxite(the white/purest in Al2O3 one) is known for the hardest mand most abrasive one, the machining of EB (EpoxyBauxite) is probably guite a no go?
Well I would rather need a precision grinding of all the mating surfaces than milling so I guess that diamond wheel grinding wouldn’t represent a problem here....
I’m just hoping for anyone here that has already done/tried something like this and can share actual experience how it went.

AS

19. Re: Moving table (fixed gantry) with two ballscrew

Hi AS - There are no perfectly round aggregates unless you use ball bearings. All of the Epoxy Granite builders use metal in areas that need post machining. All of the aggregates discussed are ceramics and would require diamond or maybe SiC type tools to machine them. They are crystalline in nature and have lots of sharp corners thats why they are excellent abrasives, plus their hardness. Something like a stonemasons setup would be needed to machine them. Usually threads etc are cast in via metal inserts or bulk metal is cast in then machined to finish. Peter

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